Error when configuring SPAN to capture trunk port data with 802.1q tag

Answered Question
Jan 20th, 2009

Hello everybody,

When I configure SPAN on my 3750 switch, it gives me this error:


% Warning: One or more specified dest port does not support requested encapsulation.


The command I use to configure SPAN is:

(config)#monitor session 1 destination interface Fa1/0/24 encapsulation dot1q

I am using WireShark as the packet sniffer and I have configured my Ether Card on my PC to accept vlan tags however I still can't see the tags from the captured data...

I also tried to configure f1/0/24 as a trunk port but I still get the same error... I will very much appreciate any help or advice! Thanks!


Correct Answer by amikat about 8 years 1 month ago


Your command should read as:

monitor session 1 destination interface Fa1/0/24 encapsulation replicate,

as documented e.g. at:,

please see the Usage Guidelines part,

Best regards,


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